Diseases and trauma involving the loss of bony tissue are the most common clinical dental problems, and we propose to develop new polymeric materials for bone tissue engineering. We hypothesize that controlling the nanoscale organization of adhesive ligands presented to transplanted cells from the polymer, as well as the susceptibility of these ligands to cell-mediated rearrangement, will regulate the gene expression of the cells. Alginate will be used as a model matrix system to address the hypothesis guiding this proposal. Cells exhibit little to no adhesion or interaction with alginate, and thus alginate provides an ideal "blank slate" on which one can confer specific cellular interaction properties in a controlled manner. Alginate also, in contrast to most model systems, is a practical biomaterial for in vivo application of this work. We specifically aim to: (1) Control the nanoscale presentation of RGD-containing peptides to a model pre-osteoblast cell line and human mesenchymal stem cells, and determine how this regulates focal adhesion formation and cell phenotype, (2) determine if the stiffness of the ligand presenting gels regulates the cells ability to rearrange the adhesion ligands, and (3) determine if these variables allow one to regulate new bone formation in vivo. The time-frame required for the gel, before it degrades, to present this information in order to regulate the cell response and bone formation will also be determined. Successful completion of these aims will have significant impact in both basic and applied sciences, and may eventually lead to improved therapies for regenerating bone defects. Establishing the mechanism by which nanoscale ligand organization and matrix mechanical properties regulate cell phenotype will provide an important new variable for design of biomaterials in tissue engineering and regeneration. The biomaterials developed in this proposal may be directly useful in therapies utilizing precursor cells to regenerate bony tissues in a variety of clinical settings.